Spatial variations of the background magnetic field (B₀) are known to cause artifacts due to spin dephasing: image distortions, signal dropouts and blurring¹. Furthermore, in the cervical spine, the nearby lungs induce large and time-varying field gradients that cannot be adequately compensated using conventional 2^nd-order spherical harmonic shim coils. Arrays of local shim coils show great promise for high-order, real-time shimming of the brain^2,3 providing an alternative to 3^rd and higher-order spherical harmonic shim coils and their attendant eddy currents, coupling, low efficiency, and expensive current drivers. However, the multi-coil shim array competes with the RF receive array for space close to the body where both arrays function with highest efficiency (assessed by RF SNR or B₀ shim offset in Hz/amp/loop-turn in the body). It was recently shown that RF and shim currents could be combined on the same conducting loop, enabling multi-coil B₀-shimming and RF reception in the same time^4,5. Moreover, these combined RF-shim coils provide similar SNR to RF-only coils at both 3T and 7T⁵. In this study, we simulate several collar-like coil array geometries for spinal cord imaging and demonstrate the potential for highly improved shimming relative to high-order spherical harmonics shimming. We also compare different designs to highlight the best one.Acquisition: Sagittal GRE field maps of ΔB₀ were acquired of the cervical portion of the spinal cord (TR = 180 ms, TE = [4.51 8.78 13.69], BW = 1736 Hz/voxel, resolution = 1.5x1.5 mm, slice thickness = 3.0mm]) with Siemens shimming parameters optimized for a large FOV (192x192 mm). For more information see [1]. Coil array design: Elliptical coils were positioned on a cylindrical frame (radius = 85 mm, height = 110mm) to fit a typical neck geometry. For the four different configurations (collar, collar-shifted, semi-collar and semi-collar shifted), several geometries were simulated (1 to 4 rows of 4 to 8 channels). For each geometry, the dimension of the elliptical coils was chosen to cover the entire (collar) or half the frame (semi-collar). In our simulations, semi-collar designs are meant to be placed close behind the neck. B₀-shimming simulation: Coil array designs were simulated using Biot-Savart to calculate the longitudinal field B_0,shim created by each coil. Shim current optimization was then performed using fmincon (MATLAB) to minimize the least-squares deviation from the uniform B₀ field⁶, ||ΔB₀+B_0,shim||², over the 5mm-wide region-of-interest (ROI) surrounding the cervical spine (7 slices). To account for practical constraints, we limited the current in each loop to 2.5amps and total current to 40amps. For comparison, shimming based on spherical harmonic functions of 2^nd to 5^th order was also simulated within the ROI. To compare shim performances, we normalized the standard deviation of the field map within the spine after simulated shimming by 2^nd order spherical harmonics shimming and then averaged this coefficient among subjects. SNR evaluation: For each voxel, relative SNR was calculated as $$$SNR = \sqrt{(R^{-1}.B_{1})^{t}.B_{1}}$$$ , where R is the noise correlation matrix and B₁ is the array of the field amplitudes created at this point by each coil. SNR was then normalized to compare different configurations’ SNR maps within a phantom (cylinder radius=65mm) and within the cervical spine (5 slices). Simulations show an overall reduction in B₀ standard deviation (STD) over the ROI as compared to 2^nd order shimming (Fig.1). With 4 rows of 4 coils, collar geometry reduces STD by 12.7 %, collar shifted by 17.3 %, semi-collar by 8.6 %, and semi-collar shifted by 14.1 %. Simulations also showed that adding coils had no significant effect on shim performance (Fig. 2). Figure 3 shows better SNR performance within the spinal cord for the collar (mean SNR = 0.0177) than for the semi-collar (mean SNR = 0.0147).This study tested different realistic configurations for combined RF-shim array coil for imaging the cervical spinal cord. It has to be noticed that not all designs preserve neighboor loop critical overlap for decoupling and would be necessary for future work. Results showed that the collar performs better than the semi-collar for SNR with comparable shim performance, however the semi-collar geometry is better adapted to various neck morphologies. The shifted configuration reveals improved performance compared to aligned coils both for collar and semi-collar array without SNR loss, as it provides additional degrees of freedom for tailoring the shim field. This study demonstrated that combined RF-shim coil arrays show considerable promise for functional imaging of the spinal cord: coil array designs promise to outperform 3rd order spherical harmonic shimming while being easier to implement in practice.